Amplification control



Sept. 3, 1935.7 c, BLACK AMPLIFICATION CONTROL Filed April 14, 1930 3 Sheets-Sheet 1 1 3mm; M M,

P 1935- K. c. BLACK 2,013,297

AMPLIFICATION CONTROL Filed April 14, 1930 5 Sheets-Sheet 2 5/0: Va/faqe on 6nd 6':

Sept. 3, 1935. K. 0. BLACK AMPLIFICATION CONTROL Filed April 14, 1950 3 Sheets-Sheet 3 Grid's G and 6' Bi yalfaqe on Patented Sept. 55, 19 35 I I UNITED STATES PATENT OFFICE AMPLIFICATION CONTROL Knox Charlton Black, Boonton, N. .L, assignor,

by mesne assignments, to Radio Corporation of America, New York, N. Y.,' a corporation of Delaware Application April 14,1930, Serial No. 444,246 I 37 Claims. (01. 250-20) This invention relates to vacuum tube ampliextensive with control grid Cl but extends befiers and particularly to methods of and apparatus tween only the portion I of grid G and the cathfor controlling the amplification of or transmisode C. sion through the amplifier. The input circuit 3 is connected through a It is the common practice to control the ampliblocking condenser 4 to the control grid and 5 fication of a vacuum tube by adjusting the opercathode, the gr d'bias voltage be ng derived from ating potential upon one of the elements, i. e., by a So e O u re 5 through potentiometer 5 varying the direct current potential existing beand the customary d s ance 1. The auxiltween that element and the cathode. I have found y grid'G1iS Connected t hat te mina Of res stthat a greater flexibility of amplification may be ance 1 which is spa from the Control grid 10 attained and, in general, with less variation of am- The direct Current a 1 the aux y grid plificatifon-eontrol voltages, when the operating is therefore the same as that on the control grid potentials upon a plurality of the tube elements but, as re a ds Signal P t the grid G is are simultaneously varied. The control voltages maintained t the cathode Potential y the ymay be varied at the same or different rates and in p Condenser The Screen grid a Plate 15 the same or opposite sense, in accordance with Circuits may be of any desired form, being here the shape of the amplification characteristic s own as ener ed f a common a y which is desired for any particular amp1ifier The special construction of the control grid re- Objects of th inve ti n ar t provide a v sults in a tube which exhibits the general characuum tube amplifier in which the control of amteIiStiCS f a high u tube at One range of D 20 plification is eifected by the simultaneous adjustetihg Velteges d e general Characteristics of ment of the operating potentials applied to a plua 10W mu e a an ra e o pe atin rality of the tube elements. More particularly, an Voltages- This yp of e s disclosed and object is to provide, in an amplifier of the type claimed y Show in his pp n Se al employing a tube having a plurality of grid ele- No. 437,225, filed March 19, 1930. The control of 25 ments, an amplification control in which the conplate Current y Section 2 of d G cttrol grid bias and the operating potential upon ihg fringing, a unct of t C t d b as another tube element are simultaneously adand is represented graphically y Curve A Of ju5ted Fig. 2. For the section I of control grid G the These and other objects of the invention will be plate Current is determined y the bias Voltages 3Q apparent from the following description, when on both the Control d G2 and the auxiliary g taken with the accompanying drawings in which:- Duet 0 the coarser spacing f t e Section I Fig 1 is a diagram of an amplifier circuit of control grid G this portion of the tube funcbodying the invention, tions as a low mu tube and, in general, the con- Figs. 2 and 3 are characteristic curves showing trol grid bi s-p current Curves are much the relationship, for different parts of the tube t than the c r sp nd u v f r t p rti n of Fig. 1, between amplification-control voltages of the tube in Which the Section 2 of d G is and plate current, located.

Fig. 4 is a family of curves showing the relation In the family of ves B to F show the between total plate current and control grid voltrelation of plate current t control grid bias 011 40 age for different alues of the auxiliary grid section I of grid G for different values of the voltage, and auxiliary grid bias, 1. e., for auxiliary grid bias Fig. 5 is a circuit diagram of. another embodil s of 5, H and I4 volts ne ative, rement of the invention, spectively. The total plate current is equal to the is In Fig. 1, the invention is illustrated in connecsu of the fi s of the bias v ta s upon the fionwith an ampiifier t T which has acathodc sections of the control grid, and its relation to 0, control grid G screen grid G anode P and ntr l d bias vo ta ma be pr s t d by auxiliary grid G The general arrangement of Combining the Characteristics o s. 2 and 3. the tube elements may conform to that of com- In Fig. 4, the curves B to F give the relationship mercial tetrode tubes having coaxial cylindrical between total plate current and control grid bias elements. v I voltage for the respective fixed auxiliary grid The control grid G comprises a winding which bias voltages noted above. is not of uniform pitch throughout its length, the When, as by means of the circuit of Fig. 1, section I being of substantially coarser pitch than the control grid and auxiliary grid are subjected the section 2. The auxiliary grid G1 is not 00- to the same amplification control potential, the 55 graph of the operating points may be plotted as dotted line H- upon the curves of Fig. 4.

Since the signal voltage is effective only upon the control grid,'and not upon the auxiliary grid, the path of operation for the signal is not the dotted line H but the full line B, C, etc., drawn throughthc line H at its intersection with the ordinate corresponding to the direct current potential upon the two grids.

Advantages obtained by this use of adjusted voltages on two tube elements will be evident from an examination of the curves of Fig. 4. It is obvious that a wide range of amplification control corresponds to 'a relatively small variation of control voltage. If the bias on the auxiliary grid remained fix-cd, or if the auxiliary grid were omitted, it would be necessary to use a much higher negative voltage on the control grid to reduce the amplification to a value corresponding, for

example, to --14 volts on the grids G and G i. e.,

to operation of the tube at the point of intersection of curves H and F. Furthermore, by an appropriate design of the tube, the distortion may be reduced when the signal is applied to but one grid and two bias voltages are controlled. This follows from the fact that the operating point of the tube travels along dotted line H as the control voltage is varied, but the amplification is determined by the full line passing through the operating point. Although the dotted line may be steep and curving rapidly, distortion will not occur if the full lines, adjacent their respective intersections with line H, are not too seriously curved.

The invention is not restricted to the manual control or to the special type of tube shown in Fig. 1.

In Fig. 5, I have illustrated the invention as applied to the automatic control of the transmission or volume level in an amplifier-demodulator system.

An appropriate input system, such as a tuned circuit I 0 impresses the incoming carrier wave signal between the control grid G and the cathode C of an amplifier tube H, and the amplified signal is passed, by a tuned coupling circuit l2 to the demodulator l3, which may be a diode. The output circuit of the demodulator preferably includes the usual radio frequency choke l4 and by-pass condenser I5, the rectified output voltage being developed across a resistance i6, and terminals l1, l8 across which an audio amplifier or other appropriate load circuit may be connected.

The rectified carrier voltage developed across the output resistance I6 is employed to efiect an automatic control of the output level of the system. The direct current bias of grid G is determined indirectly by the bias voltage on grid G and the potential difference between the two grids. The cathode of the amplifier l I is grounded for direct current and radio frequencies, and the detector circuit is grounded through condenser I9 for radio frequencies.

The tube II is provided with a space-charge grid G and, if desired, with a screen grid G The bias upon the grid G is determined in part by the relatively fixed potential of that adjustable portion of the plate supply 2| that is impressed, through adjustable tap 22, upon the plate of a direct current amplifier 23, and in part by that portion of the rectified carrier voltage across output resistance I6 which is impressed upon the direct current amplifier 23.

The cathode of amplifier 23 is connected, through a battery 24, to an adjustable tap 25 on resistance "5 and the grid is connected to the anode terminal of the resistance. The grid G of comes more negative as the carrier voltage increases. The positive direct currcnt bias on grid G is therefore reduced as the signal strength increases.

The direct current path between the control grid G and grid G may be traced through the grid resistance 21', (by-passed for audio frequency components by condenser 28), then through battery 29, the portion of resistance l6 which is included between taps 30 and 25, and battery 24 to the grid G In the absence of a signal, the potential of control grid G is more negative than that of G ,by the sum of the potentials of batteries 24 and 29. The effective bias on grid G is equal to the difierence between this potential drop and the bias on grid G When a signal is received, the effective bias on control grid G is decreased, i. e., is made less negative by the drop of rectified carrier voltage between taps 25 and 30 on resistance H5.

The direct current potentials on grids G and G are so adjusted, by choice of the relatively fixed components of the bias-voltages, that the negative bias on the control grid G2 and the positive potential on the space charge grid G will give high amplification for small signal voltages.

As the signal voltages increase, the rectified carrier voltage developed across resistance l6 operates to make the control grid bias voltage less negative and to reduce the positive potential on the space charge grid. The lowered voltage on the space charge grid reduces the amplification while the decreased bias on the control grid may have but little efiect upon the amplification. By a suitable positioning of the adjustable taps 25, 30, the relative efiects of the two amplification controlling voltages may be proportioned in any desired manner and advantage may be taken of the amplification change effected by the altered control grid bias but, in general, this will be of minor importance. The decreased control grid bias is of -major importance for its eiTect upon rent if the control grid bias remained constant,

and this tendency towards an increased flow of plate current may be reduced by decreasing the control grid bias.

The above examples are illustrative of my invention and it is to be understood that, in other circuit arrangements and with other tube constructions, the advantages noted above and/or other advantages may be obtained by the simultaneous adjustment of the operating voltages applied to a plurality of tube elements.

I am aware of the fact that a change in the operating potential applied to one tube element mayalter the effective potential between another tube element and the cathode. Such incidental alteration of an operating potential upon a second tube element is not contemplated by the present invention which comprises the simultaneous adjustment, by a deliberate change of the applied direct current voltages, of the oper-,

ating potentials upon two or more tube elements.

I claim:

1. In the operation of an amplifier circuit of the type including an audion having a plurality of grid elements, and means for establishing different direct current potentials upon the several elements, the method of controlling the amplification which comprises simultaneously adjusting the direct current potentials applied to at least two of said elements in accordance with.the strength of signals applied to the amplifier.

2. The invention as set forth in the above claim 1, wherein the potentials upon said two of said elements are varied at difierent rates to control the amplification.

3. The invention as set forth in claim 1 wherein the potentials upon said two of said elements are varied in opposite sense.

4. The invention as set forth in claim 1 wherein the potentials upon said two of said elements are varied in opposite sense and at different rates.

5. In the operation of an amplifier tube of the type having a cathode, an anode, a control grid and a. second, grid, the method of controlling the -amplification which comprises simultaneously adjusting the direct current potentials between the respective grids and the cathode in response to variations in the strength of signals applied to the amplifier.

6. In an amplifier circuit, an amplifier tube having a. cathode, an anode, a control grid and a second grid, means for establishing direct current potentials between said cathode and each of the other tube elements, means for impressing a signal voltage between cathode and control grid, and means for simultaneously adjusting the direct current potentials upon said control grid and upon another tube element in response to variations in the strength of signals impressed on the amplifier.

'7. The invention as set forth above in claim 6, wherein said potential adjusting means effects simultaneous adjustment of the direct current potentials upon the respective grids.

8. The combination with an electron discharge tube and circuit elements associated therewith to constitute an amplifier stage, said tube being provided with a cathode, anode, and a plurality of auxiliary tube elements, of adjustable means responsive to changes in the amplitude of signals impressed on said tube for simultaneously varying the operating potentials existing between the tube cathode and at least two of said plurality of the tube elements.

9. The combination with a vacuum tube having an anode, a cathode, a control grid and-an additional grid disposed between the cathode and the control grid, of circuit elements cooperating with said tube to constitute the input and output circuits of an amplifier stage, means for varying the direct current potential between said control grid and said additional grid, means for varying the bias between one of said grids and said cathode, and means insuring the simultaneous operation of said voltage varying means.

10. In a carrier wave amplifier, the combination with a vacuum tube having a cathode, an anode and a plurality of grids, of means for impressing a carrier wave signal voltage between one of said grids and said cathode, means for rectiiying the amplified output from said amplifier, and means for automatically adjusting the operating potentials applied to a plurality of said tube elements in accordance with the strength of the incoming signal.

ii. The invention as set forth in the above claim 19, wherein said automatic adjusting means comprises a resistance in the output circuit of said rectifier, c rcu t elements for impressing between said amplifier cathode .and one of said tube elements a direct current voltage proportional to the rectified carrier voltage across said resistance, and circuit elements including a direct current amplifier for impressing across two of said tube elements a direct current voltage proportional to said carrier voltage.

12. An amplifier circuit comprising an eleclron discharge tube provided with a cathode, anode, control grid, and auxiliary grid, said control grid being so constructed as to provide at least two electron streams flowing at difierent rates wiLhin the tube, means for maintaining said grids at different signal potentials, and additional means for simultaneously varying the direct current potentials of the grids.

13. An amplifier circuit comprising an electron discharge tube provided with a cathode, anode, control grid, and auxiliary grid disposed between the cathode and control grid, means for maintaining said grids at different signal potentials, and additional means for simultaneously varying the direct current potentials of the grids at different rates.

14. An amplifier circuit comprising an electron discharge tube provided with a cathode, anode, control grid, andauxiliary grid, said control grid being so constructed as to provide at least two electron streams flowing at different rates within the tube, means for maintaining said grids at different signal potentials, and additional means for simultaneously varying the direct current potentials of the grids in opposite sense.

15. An amplifier circuit comprising an electron discharge tube provided with a cathode, anode, control grid, and auxiliary grid disposed between the cathode and control grid, means for maintaining said grids at difierent signal potentials, and additional means for simultaneously varying the direct current potentials of the grids in opposite sense and at difierent rates.

16. An amplifier circuit comprising an electron discharge tube provided with a cathode, anode, control grid, and auxiliary grid, means for maintaining said .grids at different signal potentials, and additional means for simultaneously varying the direct current potentials of the grids, said auxiliary grid extending between only a portion of the control grid and said cathode.

17. An amplifier circuit comprising an electron discharge tube provided with a cathode, anode, control grid, and auxiliary grid, said control grid being so constructed as to provide at least two electron streams flowing at different rates within the tube, means for maintaining said grids at difierent signal potentials, and additional means for simultaneously varying the direct current potentials of the grids, said auxiliary grid being positioned only in the path of one of 'said electron streams.

18. An amplifier circuit comprising an electron discharge tube provided with a cathode, anode,

control grid, and auxiliary grid, said control grid blocking condenser between said input circuit and said control grid.

19. An amplifier circuit comprising an electron discharge tube provided witlra cathode, anode, control grid, and auxiliary grid, said control. grid being so constructed as to provide at least two electron streams flowing at different rates within the tube, means for maintaining said grids; at different signal potentials, and additional means for simultaneously varying the direct current potentials of the grids, said additional means including a source of direct current, a resistor in shunt with said source, a resistor connected between said grids, and an adjustable connection between said last resistor and said shunt resistor.

20. In combination with a multi-electrode tube including a cathode, anode and control grid, another electrode between the cathode and control grid, a signal input circuit connected between the control grid and cathode, an output circuit connected between the anode and cathode, means connected to the control grid for controlling the direct current potential thereof, and additional means connecting said first means and said other electrode of said tube for controlling the direct current potential of said last electrode.

21. In combination with a multi-electrode tube including a cathode, anode, auxiliary grid and control grid, the auxiliary grid= being a space charge grid between the cathode and control grid, a signal input circuit connected between the control grid and cathode, an output circuit connected between the anode and cathode, means connected to the control grid for controlling the direct current potential thereof, and additional means connecting said first means and said auxiliary electrode for controlling the direct current potential of said last electrode.

22. In combination with a multi-electrode tube including a, cathode, anode and control grid, said tube'being constructed to have a variable' mu characteristic, a signal input circuit connected between the control grid and cathode, an output circuit connected between the anode and cathode, means connected to the control grid for controlling the direct current potential thereof, and additional means connecting said first means and another electrode of said tube for controlling the direct current potential of said last electrode.

23. In combination with a multi-electrode tube including a cathode, anode and control grid, a second postive grid between the cathode and control grid, a signal input circuit connected between the control grid and cathode, an output circuit connected between the anode and cathode, means including an adjustable potential source connected to the control grid for controlling the Lirect current potential thereoftand additional means connecting said first means and the second grid of said tube for controlling the direct current potential of said second grid.

24. In combination with a multi-electrode tube including a cathode, anode and control grid, a signal input circuit connected between the control grid and cathode, an output circuit connected between the anode and cathode, a, rectifier coupled to the output circuit, means connected to the control grid and the rectifier output for controlling the direct current potential thereof, and additional means connecting said first means and another electrode of said tube for controlling the direct current potential of said last elect-rode.

25. In combination with a multi-electrode tube including a cathode, anode and control grid, a.

' signal input circuit connected between the control grid and cathode, an output circuit connected between the anode and cathode, means connected to the control grid for controlling the direct current potential thereof,.and additional means including a direct current amplifier connecting said first means and another grid electrode of said tube for controlling the direct current potential of said last electrode.

26. In combination'with an amplifier circuit including a tube provided with a cathode, control electrode, and a plurality of positive electrodes, an automatic gain control circuit comprising a rectifier having its input arranged to receive energy from said amplifier output, means for connecting the control electrode of the amplifier tube to the rectifier output, and means for connecting at least one of said positive electrodes to .the rectifier output.

27. In combination with an amplifier circuit including a tube provided with a cathode, control electrode, and a plurality of positive electrodes, an automatic gain control circuit comprising a rectifier having its input arranged to receive energy from said amplifier output, means for connecting the control electrode of the amplifier tube to the rectifier output, means for connecting at least one ofsaid positive electrodes to the rectifier output, and an electron discharge tube connected between said one positive electrode, the amplifier output and the rectifier output.

28. In combination with a radio receiver including an amplifier circuit provided with a multi-electrode tube and a detector circuit, an automatic amplifier gain control arrangement consisting of connections between at least two electrodes of said tube disposed in the electron stream from the cathode and the detector circuit output whereby the potentials of the two electrodes with respect to the cathode may be varied.

29. In combination with a radio receiver including an amplifier circuit provided with a multi-electrode tube and a diode detector circuit, an automatic amplifier gain control arrangement consisting of connections between at least two electrodes of said tube disposed in the electron stream from the cathode and the detector circuit output whereby the potentials of the two electrodes with respect to the cathode may be varied.

30. In combination with a radio receiver including an amplifier circuit provided with a multi-electrode tube and a detector circuit, an automatic amplifier gain control arrangement consisting of independent, adjustable connections between at least two electrodes of said tube disposed in the electron stream from the cathode and the detector circuit output whereby the potentials of the two electrodes with respect to the cathode may be varied.

31. In an electrical wave amplifier system, an amplifier tube, including a cathode, an anode, a.

. control grid electrode of variable mesh, a screen grid between the anode and grid, and an auxiliary grid electrode between the control grid and cathode, an output circuit between the anode and cathode, a wave input circuit between the control grid and cathode, and means for regulating the direct current potentials of said two grids with respect to said cathode.

32. In combination with a wave amplifier provided with a cathode and a plurality of cold electrodes, means for maintaining certain of the cold electrodes at a positive potential, a wave demodulator for producing a direct current potential to regulate the gain of said amplifier, and means for connecting the demodulator to at least two of said cold electrodes whereby the potentials of the latter with respect to the cathode may be varied.

33. In combination with a wave amplifier pro vided with a cathode and a plurality of cold electrodes, means for maintaining certain of the cold electrodes at a positive potential, a wave demodulator for producing a direct current potential to regulate the gain of said amplifier, means for connecting the demodulator to at least two of said cold electrodes whereby the potentials of the latter with respect to the cathode may be varied, and at least one of the two cold electrodes being at said positive potential.

34.In a signal modulated carrier wave receiving system, a tube including a cathode, an anode, a signal grid and a special gain control electrode disposed between the cathode and signal grid, a tuned signal wave input circuit connected solely between the signal grid and cathode, said signal grid being at a predetermined negative direct current potential with respect to said cathode and gain control electrode, a signal wave rectifier circuit adapted to produce a direct current voltage whose magnitude varies in response to variations in amplitude of received carrier waves, and connections between said gain control electrode and the rectifier circuit for applying said voltage to the gain control electrode in such a sense that the electrode voltage varies in a negative direction with respect to the cathode as the signal waves impressed onsaid input circuit increase in amplitude.

35. In a system, as defined in claim 34, said rectifier circuit including a diode, said tube including a positive screen grid adjacent the signal grid.

36. In a system, as defined in claim 34, said rectifier circuit being coupled to the anode circuit of said tube, and a wide range of gain control of said tube corresponding to a relatively small variation of rectifier direct current voltage.

37. In a system, as defined in claim 34:, a connection between the said signal grid and rectifier circuit for regulating the magnitude of the negative potential of said signal grid in response to said carrier wave amplitude variations.

KNOX CHARLTON BLACK. 

